Analogue Video over a laser beam

Ok, so lets scratch the DVD idea, and yes I do have glasses for use with laser, atho, it doesnt need to be a laser It can be a good old high brightness LED, as It does only need to travel 12 inches.

AnalogKid said:

Performance parameters: differential gain, differential phase - ?

Both amplitude modulating a laser diode and receiving the laser energy with a photodiode or phototransistor are *very* non-linear processes. Also, we're talking about a 10 MHz signal bandwidth. (4.2 MHz plus some margin to minimize phase distortions). What is your skill set for this type of circuit?

ak

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what were you thinking?

Nigel;

Perhaps my suggestion of modulating the baseband video has no validity, but with the scarce information provided, my recommendation may be as valid or as absurd as anyone else.

For the modulation portion, however.....
I know that in the 1980s and 1990s the analog TV architectures between Europe and America had some subtle differences. I can tell you that every VCR, Cable TV box or Video game I ever saw on this side of the pond had the RF output to the TV being handled by an IC, like the image below.

I have a personal anecdote with this particular IC. In the late 1980s I worked for a Cable box manufacturer and we were using a Japanese modulator IC, if I recall correctly from Toshiba. We were producing over 2 million units per year and believed we were an important customer.

Well, one day Toshiba came to us and suddenly announced that Nintendo, who was also their customer for this particular IC, had ramped up its requirements and as such all of the modulator IC's production would now go to Nintendo. Effective immediately. No last time buy.
So sorry, but the Keiretsu members are priority.

So we had to scramble to find out a suitable replacement and found this Korean device, from Samsung. I had to develop the test methodology to validate the changeover, so I worked many nights and weekends to perform the all the testing.

schmitt trigger said:

Nigel;

Perhaps my suggestion of modulating the baseband video has no validity, but with the scarce information provided, my recommendation may be as valid or as absurd as anyone else.

For the modulation portion, however.....
I know that in the 1980s and 1990s the analog TV architectures between Europe and America had some subtle differences. I can tell you that every VCR, Cable TV box or Video game I ever saw on this side of the pond had the RF output to the TV being handled by an IC, like the image below.

I have a personal anecdote with this particular IC. In the late 1980s I worked for a Cable box manufacturer and we were using a Japanese modulator IC, if I recall correctly from Toshiba. We were producing over 2 million units per year and believed we were an important customer.

Well, one day Toshiba came to us and suddenly announced that Nintendo, who was also their customer for this particular IC, had ramped up its requirements and as such all of the modulator IC's production would now go to Nintendo. Effective immediately. No last time buy.
So sorry, but the Keiretsu members are priority.

So we had to scramble to find out a suitable replacement and found this Korean device, from Samsung. I had to develop the test methodology to validate the changeover, so I worked many nights and weekends to perform the all the testing.


View attachment 126138

View attachment 126139

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That is very cool, thanks for the interesting story

schmitt trigger said:

Nigel;

Perhaps my suggestion of modulating the baseband video has no validity, but with the scarce information provided, my recommendation may be as valid or as absurd as anyone else.

Click to expand...

It's a bit 'backwards' - you're not 'modulating the broadband video', you're AM modulating the 'RF carrier' - perfectly valid if you're using RF.

For the laser requirement you could do the same, as long as the laser diode (and the receiver) can be modulated in turn by the RF carrier frequency.

It's a bit like IR remote controls - where you modulate a higher frequency carrier (about 40KHz) with the data, and that in turn is used to modulate the IR LED.

A slightly different scheme would be to FM modulate an RF carrier with the video, which might be better due to the non-linear response of a laser diode?, and this was how VCR's worked to record to the tape. But again, it requires the optical system to be able to cope with the RF modulation frequency used.

For the modulation portion, however.....
I know that in the 1980s and 1990s the analog TV architectures between Europe and America had some subtle differences. I can tell you that every VCR, Cable TV box or Video game I ever saw on this side of the pond had the RF output to the TV being handled by an IC, like the image below.

Click to expand...

VCR's etc. were built down to serious price constraints, so were usually far cruder than then using an IC, although a few did use them over here - another reason they weren't commonly used is as you found out - limited availability, with other manufacturers having priority. If you google 'video rf modulator schematics' there are countless examples, some using IC's, but most not. Many were remarkably simple, and obviously cheaper than buying an IC and special oscillator/crystal. I was quite amused to see a schematic for the modulator in the Commodore Plus4 on the google search, I still have one of those

Any large consumer manufacturer usually will only use components if they have multiple sources for it, or at least an absolutely guaranteed availability from the single manufacturer. This was why Grundig was one of the last to use IR receiver IC's, as for a long time there was only a single manufacturer.

But as regards the requirement here, I suspect he's looking for a far simpler solution than is likely to be possible?.

Wow, Nigel...
I Googled it, this Commodore schematic is awesome! (actually DuckDucked it, but it is cumbersome to write.)

I imagine that the input labeled "AUDIO" is not baseband audio but actually subcarrier audio.
5.5 Mhz in the UK.

One thing that was very common in these old analog circuits is the sheer number of required adjustment: trimpots, trimcaps and adjustable inductors.

schmitt trigger said:

Wow, Nigel...
I Googled it, this Commodore schematic is awesome! (actually DuckDucked it, but it is cumbersome to write.)

I imagine that the input labeled "AUDIO" is not baseband audio but actually subcarrier audio.
5.5 Mhz in the UK.

Click to expand...

Wrong on a couple of counts, UK inter-carrier is (or at least was) 6MHz, 5.5MHz was used on the Continent. You wouldn't believe how many TV's I've converted over the decades, either to 6MHz for sets coming in, or to 5.5MHz for sets going out.

The AUDIO connection is simply an audio signal, Q4/L8 is an RF oscillator (6MHz for the UK), FM modulated by the audio signal.

That circuit is certainly overly complicated though, and well 'littered' with filtering.

If I had to design a project needing a modulator from scratch, I'd have used the IC as you did - or MUCH more likely (and what most manufacturers did) simply buy in a ready made 'tin box' module.

Thanks for setting me straight.... 6 Mhz indeed!

And let's not forget that the French SECAM actually used AM modulation for the audio subcarrier, instead of FM for NTSC or PAL.

Ok, so I figured out a way to do this, with my own tiny little brain.
There are composite audio video in composite A/V output units, transmission over Fibre Optic sold for security purposes. Hopefully this will work.

kimbear said:

Ok, so I figured out a way to do this, with my own tiny little brain.
There are composite audio video in composite A/V output units, transmission over Fibre Optic sold for security purposes. Hopefully this will work.

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I refer you to post #4

If I might suggest, IR can do that and there are loads of turnkey devices online for both the transmission and reception. Nearly plug and play for you.
Last time I played with such was laser spy audio detecting acoustic reflections from windows or walls. Video would be similar with a 4 Mhz bandwidth.
Transmitting you use a pizo transducer fed by video, reflecting the laser in any flavor you like.
Receiving is a simple laser detector and video amp.
Please note the precautions in other reply's